(a) Field of the Invention
The present invention relates to an automatic transmission, and more particularly, to a parking apparatus of an automatic transmission that enables a parking rod to be easily disengaged from a parking gear, thereby making it easy a select lever to move from P range to another range more smoothly, especially when the car is on a slope. The present invention further relates to a method for controlling such a parking apparatus of an automatic transmission.
(b) Description of the Related Art
Most of the well-known automatic transmissions are provided with, in addition to a general parking brake, a parking apparatus to prevent the car from moving by locking the parking gear in a parking xe2x80x9cPxe2x80x9d range, the parking gear being fixedly mounted around the output shaft.
When the select lever is shifted to the P range, a parking rod linked to the lever activates a sprag so that an end of the sprag gets inserted into an indent formed on an outer circumference of the parking gear, which accordingly locks the parking gear.
FIG. 5 shows a conventional parking apparatus.
A detent plate 100 is formed to push a parking rod 102 when the select lever (not shown) is shifted to a P range. When the detent plate 100 pushes the parking rod 102, the parking rod 102 lifts a proximal end of a sprag 108 with a roller 104 moving rightward along a roller support 106.
Accordingly, a distal end of the sprag 108 falls with its projection 110 being inserted into an indent 114 formed on an outer circumference of a parking gear 112 so that the parking gear 112 is locked.
A return spring 116 is disposed at a pivot axis of the sprag 108 to bias the distal end of the sprag 108 upward.
In operation, when a car is parked on a slope, the car moves slightly downhill so that the parking gear 112, fixed around an output shaft of the transmission, rotates a small amount equal to a clearance between the projection 110 and a side wall defining the indent 114.
Resultantly, the projection 110 inserted in the indent 114 comes into tight contact with the side wall, forming a high frictional force between the projection 110 and the side wall. The high frictional force causes a problem that easy movement of the select lever from a parking P range to another range is prevented.
The present invention has been made in an effort to solve the above problem of the prior art.
It is a first object of the present invention to provide a parking apparatus that is designed such that a parking rod can be easily disengaged from a parking gear so that a select lever can shift easily from a P range to another range.
It is a second object of the present invention to provide a method for controlling a parking apparatus which a select lever can shift easily from a P range to another range.
To achieve the above first object, the present invention provides a parking apparatus comprising:
a parking gear assembly comprising an inner rotating member fixed to an output shaft of the transmission and an outer rotating member with indents formed on an outer circumference, the outer rotating member being rotatably disposed around the inner rotating member;
a parking rod assembly comprising a projection, the projection being interlocked with one of the indents in a parking xe2x80x9cPxe2x80x9d range; and
means for generating a rotational displacement between the inner rotating member and the outer rotating member when the projection is released from the indent.
The means for generating rotational displacement of the parking apparatus comprises:
a cylinder to which fluid pressure is supplied through a fluid path connecting the cylinder and an fluid gallery formed along an axis of the output shaft, the cylinder being formed inside of the inner rotating member;
a piston activated by the fluid pressure, the piston being disposed inside of the cylinder;
a key hole, of which the shape is trapezoidal, formed inside of the outer and inner rotating members, a larger diameter of the key hole being formed in the outer rotating member; and
a sliding key, of which the shape is also trapezoidal, disposed in the key hole with a restoring spring between larger surfaces of the sliding key and the key hole.
To achieve the second object, the present invention provides a method of controlling a parking apparatus comprising an inner rotating member fixed to an output shaft of a transmission and an outer rotating member with indents formed on an outer circumference, the outer rotating member being hydraulically rotatable at a predetermined displacement with respect to the inner rotating member, the method comprising the steps of:
(a) determining if a select lever is in a P range;
(b) determining if a foot brake is operating when the select lever is in P range;
(c) supplying fluid pressure to rotate the outer rotating member with respect to the inner rotating member at the predetermined displacement when the foot brake is operating;
(d) determining if the select lever is shifted to another range;
(e) discontinuing the fluid pressure supply when the select lever is shift to another range;
(f) determining if the vehicle velocity equals zero;
(g) determining if the select lever is in the P range hen the vehicle speed equals zero;
(h) determining if the foot brake is operating when the select lever is in the P range;
(i) determining if the engine is stopped.
The method further comprises the steps of:
(j) determining, when the select lever is not shifted from the P range to another range in the step (d), if the foot brake is operating; and
(k) discontinuing the oil pressure supply and returning to the step (a).